The present invention relates to a method of manufacturing an IC device, and more particularly to a method of manufacturing a Schottky diode device.
Schottky diodes are used widely in electronic systems such as amplifiers, receivers, control and guidance systems, and power and signal monitors, and as rectifiers and clamps in RF circuits. Commercial applications include radiation detectors, imaging devices, and wired and wireless communication products. Generally speaking, high frequency Schottky diodes may be GaAs devices. Certainly, RF Schottky diodes can also be silicon devices, which may be integrated in silicon ICs.
FIGS. 1(a)-1(h) illustrate a method of manufacturing a Schottky diode device according to the prior art. As shown in FIG. 1(a), a gate oxide layer 12 and a polysilicon layer 13 are formed on a substrate 11 sequentially. Then, an oxide layer 14 is deposited on the polysilicon layer 13, as shown in FIG. 1(b), by means of a chemical vapor deposition (CVD) process for protecting the MOS region of the device while the follow-up implantation process is performed. A photoresist layer 15 is deposited on the oxide layer 14, and then a part of the photoresist layer 15 is removed via a lithography process thereby obtaining the photoresist layer 15 with the demanded patterns, as shown in FIG. 1(c). Through the patterned photoresist layer 15, a buffered oxide etch (BOE), i.e., an isotropic wet etch, is executed to the oxide layer 14, as shown in FIG. 1(d), and the resulted structure is shown in FIG. 1(e). Then, a dry etch process is performed through the photoresist layer 15 to etch the polysilicon layer 13 and the gate oxide layer 12 for defining the MOS region, as shown in FIG. 1(f). Having developed to this point, the photoresist layer 15 can be removed. After the photoresist layer 15 is removed, an ion implantation process is executed to form the implanted regions in the substrate 11 and the polysilicon layer 13, as shown in FIG. 1(g), using the trapezoid structure of the oxide layer 14 formed after the BOE process as a mask. The problem of electric leakage can be overcome by means of forming the implanted regions in the implantation process using the trapezoid structure of the oxide layer 14 as a mask. Finally, a metal conducting layer 16 is formed on the above structure, as shown in FIG. 1(h), to complete the Schottky diode device.
However, in practice, since a CVD-deposited oxide layer is introduced into the above manufacturing process, the photoresist layer cannot adhere to the oxide layer well. Therefore, the photoresist layer would easily lift and peel from the CVD-deposited oxide layer in the BOE process, thereby influencing the features of the final structure. FIGS. 2(a)-2(h) illustrate another method of manufacturing a Schottky diode device according to the prior art. As shown in FIG. 2(a), a gate oxide layer 12 and a polysilicon layer 13 are formed on a substrate 11 sequentially, and then an oxide layer 14 is deposited on the polysilicon layer 13, as shown in FIG. 2(b), by means of a chemical vapor deposition (CVD) process. Subsequently, a photoresist layer 15 is formed and defined on the oxide layer 14 by means of a lithography process. Since the adhesion between the photoresist layer 15 and the CVD-deposited oxide layer 14 is poor (as shown in FIG. 2(c)), the photoresist layer 15 is easy to peel off during the follow-up BOE process, i.e. an isotropic wet etch process, as shown in FIG. 2(d). If the photoresist layer 15 peels off, the oxide layer 14 will be overetched and a trapezoid structure cannot be formed, as shown in FIG. 2(e). Moreover, in the follow-up dry etch process, the oxide layer 14 will be removed completely via a blanket etch, as shown in FIG. 2(f). Accordingly, a complete Schottky diode device cannot be obtained when the following ion implantation and formation of the metal layer 16 are performed on the above structure.
From the above, a wide and thick photoresist layer disposed on a narrow substrate often suffers the lifting issue in the BOE process, i.e. an isotropic wet etch process. Particularly, for the CVD film produced in an atmospheric or a sub-pressure process, it has low surface energy with photoresist, so the adhesion between the photoresist layer and the CVD film is poor. FIGS. 3(a)-3(b) show the SEM photographs of abnormal lifting photoresist according to the prior art. The photoresist layer 15 lifts, and even peels off, from the surface of the oxide layer 14 due to the low surface energy between the oxide layer 14 and the photoresist layer 15. Such poor adhesion will influence the following defining of the ion implanted region, and the etch direction and the residual thickness of the wet etch process, and even damage the electrical performance of the devices.
Therefore, there is a need to provide a method of manufacturing a Schottky diode device through adjusting the manufacturing process without increasing the cost.